Apparatus for gas analysis



April 3, 1952 w. M; ZAIKOWSKY 2,591,761

APPARATUS FOR GAS ANALYSIS I Filed June 14, 1946 w 2 SI-lEETS-SI-IEET 1 22a 35 35/ 38/ EFT 3 5 M A /06 B Am J ,/2/ /27 /8 7 490 M9 M6 A92 I INVENTOR.

ATTORNEY April 3, 1952 w. M. ZAIKOWSKY 2,591,761

APPARATUS FOR GAS ANALYSIS Filed June 14, 1946 2 $HEETSSHEET 2 22/ ii 0 22a INVENTOR WLADIMIR M. ZAIKOWSKY ATTORNEY Patented Apr. 8, 1952 APPARATUS! FOR GAS ANALYSIS! Wladimir M. Zaikowsky, Pasadena, Calif., assignor to Nina D. Zaikowsky Application June 14, 1946, Serial No. 676,819

8 Claims. (Cl. 7327) This invention relates broadly to measuring methods and apparatus which are particularly useful in connection with, although they are not limited to, gas analysis.

A specific application of the invention is to gas analysis in which it is desired to produce a single reading which will continually indicate the concentration of one component as the result of measurement of the concentrations of two or more related components. In that sense the present invention represents a further development of the methods disclosed in my copending application, Serial No. 564,645, filed November 22, 1944 for showing the amount of oxygen necessary for complete combustion of hydrocarbons by the integration into a singl reading of the effects produced separately by carbon dioxide and water resulting from combustion.

An object of the invention is to provide improved bridge circuits for facilitating measurements of both the summation effects and the difference effects of two resistances that are subjected to conjugated or mutually dependent variations,

Another object of the invention is to provide bridge circuits that facilitate the comparison of a plurality of pairs of resistances and the comparison of the individual resistances composing said pairs.

Another object is to provide bridge circuits containing a plurality of resistances of different predetermined sensitivities, whereby the bridge circuits are capable of reducing a plurality of conjugated effects to a common scale.

Another object is to reduce to a common scale the cooling effects of gases having different thermal conductivities, whereby said effects can be integrated by means of identical temperaturesensitive resistors in a common bridge circuit.

Still another object is to extend the general methods of analysis disclosed in my aforementioned prior application Serial No. 564,645 to the measurement of parent substances by measurements on gaseous components resulting therefrom, where the gaseous components have thermal conductivities that are not equally proportional to the amounts of the parent substances required for their formation.

Other more specific objects and features of the invention will appear from the description to follow.

The prior application, Serial No. 564,645, discloses a method of measuring the amount of oxygen required for complete combustion of hydrocarbons by integrating the effects of the thermal- 1 conductivities of the water and the carbon dioxide resulting from combustion.

As pointed out in that application, in the case of hydrocarbons, the total effect on the thermalconductivity of the water produced by the conproduced by the gaseous components resulting from combustion is equal to the ratio between the volumes of oxygen consumed in their formation.

In accordance with th present invention, the bridge circuit described in the prior application, Serial No. 564,645, is adapted to effect similar measurements when the mentioned equality of proportions does not exist. This greatly extends the usefulness of the circuits of said prior application because, generally speaking, two parent substances, gaseous or solid, often result in the formation of a gas having two or more gaseous components that will produce efiects on the thermal-conductivity of the gas that are not equally proportional to the amount of the parent substances consumed in their formation; and in certain cases, the product of interaction may contain gases that do not include the parent substance to be measured at all and yet are characteristic of the amount of said parent substance.

In part, the present invention resides in methods and apparatus for varying the relative effects of gases on different temperature-sensitive resistors in a bridge circuit and includes several different Ways of obtaining this result.

One way is to provide a bridge circuit in which the sensitivity (to the cooling effect of a gas) of resistors in one pair of opposing arms of the bridge is different from the sensitivity of another pair of resistors in opposing arms. Th different sensitivities may be obtained by exposing only a portion of the resistors constituting opposing arms to the gases. Thus, the resistor in a test cell containing a gas to be tested may be connected in series or in shunt to another resistor that is not exposed to the particular gas that is in the test cell.

Another way is to provide a bridge circuit in which the effect on a temperature-sensitive resistor of a gas under test is reduced. This may be accomplished in either of two ways. One way is to dilute the gas under test with an inert gas before delivering it to the test cell or cells in certain arms of the bridge.

Another way is to provide a difiusion passage between two cells in opposing arms of the bridge, so that there is a limited interchange of gas by diffusion between the two cells and hence, a partial reduction of the differential between the thermal-conductivities of the two gases.

The present invention includes various features which increase the general usefulness of bridge circuits.

One feature is the provision of a reversing switch for reversing the positions in the bridge of two opposing arms. In one position of the reversing switch, the effects of one pair of opposing arms is additive with respect to the other pair of opposing arms, while with the switch in its' other position the effect on thebridge circuit of one pair of opposing arms is subtractive with respect to the other pair of arms. This arrangement may be used to add the effects produced by four gases, irrespective of whether the signs of the thermal-conductivities of the gases applied to the respective pairs of cells are the same or opposite.

Another feature of the invention is a single bridge circuit that can be readily converted into two separate bridge circuits for comparison of gas-sensitive resistors against auxiliary resistors that are not affected by the gas, with current dividing resistors for balancing the separate bridge circuits. 7

Another feature of the invention is a bridge circuit having auxiliary resistors which can be used in combination with temperature-sensitive resistors for providing either two separate bridge circuits or a single bridge circuit, with provision for cutting out the auxiliary resistors to thereby increase the sensitivity of the bridge and automatically cut in additional series resistance to maintain the current constant in the bridge.

' Still another feature of the invention is single bridge circuit in combination with switching facilities for readily forming two different bridge circuits in place of a single bridge circuit and measuring two different gas components with the use of the same galvanometer. I 7

Various other more specific objects and features of the invention will become apparent from the detailed description to follow with reference to the drawing, in which:

Fig. 1 is a schematic diagram of a system in accordance with the invention; 1 K

Fig. 2 is a simplified schematic diagram illustrating one condition of the electric circuit of Fig. 1 and an alternative gas ciriuit;

Fig. 3 is a simplified schematic diagram showing the electric circuit of Fig. 1 in still another condition of adjustment and showing still another gas circuit.

Eig. 4 is a schematic diagram showing a system alternative tothat of Fig. 3; and

Fig. 5 is a schematic diagram showing a system alternative to that of Fig. 1.

In Fig. 1, four temperature-responsive, electrically heated resistors 35I,.36l, 3H and 33I are positioned in four test cells 35, 36, 31 and 38, respectively. Such testj cells may, for example, be of the type which is disclosed and claimed in my 'Patent No. 2,506,535 which issued Maya," 1950.

The resistors 35] and 36I-are in opposing arms "of one bridge circuit, Xf and theirs-sistors 3H and 33 I are in opposing arms of a secondbridge circuit, Y. The resistors 35I and 3'6 I 'areint erconnected by a tapped resistor IOI "having an a'djustable tap I02, whichis'connected through a resistor I03, a variable resistor I04, and a milductor I I5' to the resistor H3.

pair of fixed resistors Il2-and I I3. Furthermore,

one end of resistor I I0 is directly connected by a conductor II4 to one end of the resistor II2, and the resistor II I is directly connected by a con- Various points on the bridges X and Y are connected to contacts of a multiple position switch H6, so that by shifting the switch into different ones of five positions, different circuits can be obtained. The

five positions of the switch II6 are identified by the letters A, B, C, D and E, respectively.

Position A is an inactive position, in which contacts II! of the switch, which are connected to a pair of conductors II8, are disconnected from both the bridges X and Y. It will be-observed that the conductors II8 are adapted to be connected by a reversing switch lI9 to a meter I20. During a test, the switch IIB'is adjusted into position B, C, D or E.

When the switch II6 is'moved into position B, the resultant bridge circuit includes the resistors 35I, 36I, H0 and III in the four arms of the bridge, with the meter I20 connected between the junction' I2I of" the resistors 3'uI and H3 and the junction I22 of the resistors 35I and III. Thus, when the switch IIBis in position B, the contacts II I are connected directly to contacts I23 and I24, which are connected to'the junctions I22 and I2I, respectively, and the conductors H4 and H5 are short circuited at the switch contacts I25 and I26. It will be observed that the connection from the short-circuited conductors I I4 and H5 to the tap I08 is completed through the bridge Y, but this'does not afiect the balance of the bridge X. I

In position C, all the conditions are the same asin position B, exceptthatthe meter I20 is connected across the junctions I21 and I28 by switch contacts I20 and I30,'respectively, and the connections to the meter are reversed as compared to the connections in position B.

When switch I I6 is moved into position D, the bridge circuit contains both the resistors 36I and H0 in one arm'of the bridge, the resistors 35I and III in the adjacent arm of the bridge, the resistors II2 and 38I in the third arm of the bridge, and the resistors I I3 and 37 I in the fourth arm. It will be noted that in pQSition D the switch 6' no longer short-circuits the conductors I14 and II5 through contacts I25 and I26, but, instead connects these conductors through contacts I3I and I32 to the meter I20.

In position E of switch II6, the bridge circuit includes only the cell resistors 35 I, 36I, 3' and 38I in the respective arms of the bridge, and the meter I20is reversed with respect to its connection in position l). Thus, it will be observed that i the meter contacts I I! are connected to contacts junctionIZ'l of bridge Y" andthe junction I2I of bridge X.

It will be observed that in positions A, B, C and D the switch contact I38 interconnects a pair of arcuate contacts MI and I42, which are connected to opposite ends of the resistor I03. This functions to automatically remove the resistor I03 from the circuit and thereby increase the potential applied between the taps I02 and I08 when all eight of the bridge resistors are in the circuit. However, in position E the fixed resistors H0, III, H2 and H3 are removed from the circuit, and it is to compensate for the resultant reduction in the total resistance of the bridge that the resistor I03 is introduced.

The above bridge circuit is particularly useful in combination with a particular type of gas analysis apparatus for which my separate patent application, Serial No. 676,820 was filed simultaneously herewith, on June 14, 1946. Said application shows a convenient way of supplying two pairs of cells with three or more different gases, and it may be assumed, in a joint reading of said two applications, that the four temperature-sensitive resistors shown in said apparatus correspond to the four temperature-sensitive resistors of the circuits shown herein.

It is sometimes desirable to successively manipulate the switch II6 to produce the four different connectionscorresponding to positions B, C, D and E during successive steps in a single analysis. As an example, the bridge circuit of the present invention is particularly well suited for the practice of the method described in my copending application, Serial No. 564,645, filed November 22, 1944 with reference to Fig. 1 of the drawing in that application. The above-mentioned application discloses a method of determining, by thermal-conductivity measurements on exhaust gas, the oxygen equivalent of both the water and the carbon dioxide in the exhaust gas. In practicing the method with the present bridge apparatus, cells 35, 36, 31 and 38 of the present application would be substituted for cells Illa, I2a, I3a. and Ila, respectively, of the prior application.

Under the conditions outlined, cell 35 would contain normal exhaust gas containing bothwater vapor and carbon dioxide; cells 36 and 31 would contain exhaust gas from which the water had been removed but in which the carbon dioxide was still present; and cell 38 would contain exhaust gas from which both the water and carbon dioxide had been removed.

By moving the switch II6 into position B, the resistor 35I, exposed to normal exhaust gas, would be compared against resistor 36I, which is exposed to dry exhaust gas, thereby enabling the determination of the water content of the gas.

By moving the switch II6 into position C, the resistor 3'II, exposed to dry exhaust gas, would be compared against the resistor 38l, which is exposed to exhaust gas from which both the water and carbon dioxide have been removed, thereby enabling the determination of the carbon dioxide content of the exhaust gas.

By moving the switch II6 into position D, the resistor 35I, exposed to normal exhaust gas, and the resistor 38I, exposed to exhaust gas from .which both the water and carbon dioxide had been removed, would be connected in opposite arms of the bridge so that they would produce a cumulative effect. The resistor 36l and the resistor 3II, both of which are exposed to dry exhaust gas, would be connected in the other two arms of the bridge and produce a cumulative 6 effect. The net effect of the resistors 35I, 36I 3H and 38! would be to produce a reading of the meter I20 indicative of the oxygen equivalent of the sum of the water and the carbon dioxide in the exhaust, as fully explained in said application, Serial No. 564,465.

It will be observed that a reversing switch 210 is provided in the bridge circuit Y between the fixed resistors H2, H3 and the temperaturesensitive resistors 3H and 38L By means of this reversing switch, the two pairs of opposing temperature-sensitive resistors 35I, 36I and 3H, 38l, respectively, may be connected so as to add the changes of potential produced by each individual pair, or they may be connected so as to subtract the potential produced by one pair from the potential produced by the other pair. In the first case, these two pairs of resistors serve to add the effects produced by four gases if the effects of each pair of gases are of the same sign (that is, :both plus or both minus). On the other hand, if the effects of the two pairs of gases are opposite, then in order to produce the summation of the efiects the relative position of said two pairs of resistors is reversed by means of the switch 210.

The separately adjustable current-dividing resistors IOI and I09 at opposite ends of the single bridge circuit are particularly useful in that when the single bridge circuit is divide-d into two bridge circuits, any unbalance between each air of opposing temperature, sensitive resistors can be separately balanced or neutralized. Thereafter, when the switch I I6 is shifted to combine the two bridge circuits into a single bridge circuit, one may be assured that the single bridge circuit is balanced not only at the neutral points but is also balanced on each side. The provision of the two current-dividing resistors insures that only potentials produced by the effects of the thermalconductivity of the gas on the temperature, sensitive resistors will be added or subtracted, according to the position of the reversing switch.

The above-described elements of my bridge circuit are further useful because they permit, merely by operation of the reversing switch 210, the obtaining of either the sum of or the difference between the two unknown potentials produced by each pair of temperature-sensitive resistors.

Thus, assigning to said two unknown values of potential th symbols of a: and g, respectively, and assigning the symbols a and b to the values of the readings obtained in said two positions of switch 210, there results a set of two linear equations with two unknowns:

Consequently, in a Well known manner, the value of :1: and y can be obtained from said two equations. In other words, the above circuit elements permit not only the obtaining of the integrated effect of two unknown individual eifects, but, as well, permit the evaluation of each of said individual effects.

As has been already explained, the two pairs of auxiliary resistors IIO, III and H2, H3, respec- .tively, are useful for the check of balance between the two temperature-sensitive resistors forming each pair. However, after this task is performed, it is often undesirable to have them in the bridge circuit. For example, they increase the total resistance of the bridge and decrease its sensitivity. In my circuit, provisions are made to short-circuit said auxiliary resistors after they 7 serve their useful purposes bymoving' the switch I I6 into position E. It will be apparent that each pair of opposing auxiliary. resistors I I0, II I and I I2, I I 3 should be carefully balancedindividually, and the sum resistance of resistors I10 and I I2 should be equal to the resistance of resistor I03.

The combination of the reversing switchzlll with the dividing resistors ISI andIIlil permits individual balancing of each pair of opposing arms when switch E IE is in position'E and the auxiliary resistors are short-circuited, as followsiIn either position; of switch 278, the bridge is first balanced disclosed in my copending patent application," Serial No; 672,472 filed May 27, 1946.

Thus, there is shown schematically a combustion device I51 having a fuel-air ratioadjusting handle I52 movable over a graduated scale I53, whereby the fuel-air mixture can be made rich or lean to equal extent. Exhaust from the combustion device I5I flows through a conduit I54 and a portion of the exhaust is diverted into'a branch conduit 1 I55. Inserted in the conduit 155 is a gas conditioner I56 which maybe of such construction as to remove everythin from the exhaust gas except oxygen and combustible gases.

After leaving the conditioner I55, the gas passes through a restricter I51 and into two branch conduits I53 and I59, respectively. The branch conduit I58 is connected in turn to two branch conduits I63 and I68 through which it flows into a common duct I73.

The branch conduit I 63 is connected to the gas cell 35 and the branch conduit Hi l-is connected to the gas cell 38. A treating chamber I 65, which may contain copper oxide is positioned in the conduit I63 ahead of the cell 35, and it maybe heated by any suitable means; which, in this-instanceis an electrical resistance element I66 energized by current from a battery I61.

The branch conduit E59 feeds into two branch conduits I63 and I69, respectively, to which the test cells 37 and 38 are respectively-connected. -Both the conduits IE8 and M59 feedinto the duct 13. A treating chamber H9 is positioned in the conduit H59 ahead of the cell 38 and may contain carbon and be heated-by a resistor Ill energized by current from a battery I72.

It will be observed that a conduit I 60 is connected to the branch conduit I58 and is adapted tosupply air thereto through an adjustable restrictor I62 and a valve I6 I 'The special purpose of elements H59, 16! and I962 will be described later and in the meantime it may beass'umed that the valve I6! is closed.

There is also shown a passage 213" in'terco11- necting the cells 35 and-SE and containing a valve ll'. "The purpose of this valved passage will be described later and for present purposes'it"may be considered that the valve is-closed to segregate the cells 35 and 35 each from the'other;

Assuming that the treating' ch'amber IEE contains hot copper oxide, rich exhaust gas (containing unburned combustible) will be altered in passhaust of a' leanmixture.

;the-o'ther -han d, when themixture is lean,the ex' haust gas will contain no unburned combustible that would be affectedby hot copper oxide, so that the gas in cells 35and'36 willhave the same composition.

In contrast, hot carbon in the treating chamber Illlwill be consumed by the oxygen in a lean mixture, so that the gas in cell 38 will differ from the gas in cell 31. On the other hand, when the mixture is rich, the-exhaustwill be unafiected by hot carbon inthechamber I-Idand thecells 31 and 38 will contain gas of the same composition.

It will be apparent, therefore,that when the exhaust'is lean onlythe temperature-sensitive resistors '31! and 38I will develop a potential, whereas when theexhaust is rich,- only the temperature-sensitive resistors 35I and-36l will deexhaust gas treated-with hot carbon. However, the present systemdiffers from'that of the lastmentioned application in'that it depends on the simultaneous use of threesor more different gases in four different test cells, the four temperaturesensitive resistors of whichare included in a single bridge circuit.

The present system has-the advantage over the system of application Serial No. 672,472 in that it does not require a meter ofbiasedsensitivity in order to' give equal deflections for rich and lean mixtures.

In accordance with the present invention, the need for a biased sensitivity meter can be. eliminated by the provision'of'suitable shunts connecteduacross the temperature-sensitive resistors '35I and 36ILand these shunts will be described next. 1

As has been pointed out indetail in my copending application, Serial No:672,472, ordinarily the sensitivity of a thermal-conductivity cell to the exhaust ofJa rich mixture is much greater than its sensitivity tothe'exhaust of a'lean mixture, because a rich mixture usually contains hydrogenwhi'c'h has a very high thermal-conductivity, whereas no hydrogen is present in the ex- In1 thecircuit shown in Fig. 1, equalization of response tori-ch and lean mixtures can be obnot exposed to the gases in the cells 35 and 36. It is essential that both the'temperature-sensitive'resistors 35I and 36I be shunted by resistors of the same value, and tomake the apparatus flexible for use in making tests on various gases,

the shunt resistors should be continuously variablein equal degree. 7 7

"To obtain this result, I show in Fig. 1 separate shunts for the resistors 35I and 36I which are adjustable and mechanically coupled together so that" the sensitivities of the resistors 35I and .ing therethrough, so that for air'ich mixture the, "36I may be reduced in-equal degree in a plurality f g'as' in cell 35 will differ'fro'ni that incelltfi."On IFO E Thus, there are provided for connection in.

shunt to the temperature-sensitive resistor 35I, a resistor I15 and a resistor I16. The value of the resistor I15 is fixed, but the amount of the resistor I18 that is included in the circuit can be varied by means of a slide I11. A switch I18 is provided to open the shunt circuit when the sensitivity of the resistor 35I is not to be reduced. The temperature-sensitive resistor 35! is likewise adapted to be shunted by a pair of resistors I80 and I8 I the latter having an adjusting slide I82 for adjusting its value. A switch I83 is provided for connecting the resistors I80 and I8I in and out of circuit.

It will be observed that both of the slides I11 and I82 are mechanically supported on a common framework I84 for movement simultaneously to equal extent. Furthermore, the extent to which the resistors I16 and I8I are included is indicated by a pointer I85 movable over a scale I88.

shunting of the temperature-sensitive resistors 35I and 38I by the resistors I15 and I16 and the resistors I80 and I8I, respectively, may produce an appreciable change in the total resistance of the bridge circuit, and to maintain the total resistance constant and also maintain the resistance of each arm of the bridge constant, I may provide an auxiliary resistor I81 which can be adjustably included in series with the temperature-sensitive resistor 36I and an auxiliary resistor I88 which can be adjustably included in series with the temperature-sensitive resistor 35. Thus, one end of the resistor I81 is connected permanently to one end of the resistor 36I, but

is connected to one end of the current-dividing resistor IN, by a Slide I89. The resistor I88 likewise is permanently connected at one end to one end of the temperature-sensitive resistor 35I but is adapted to be connected througha slide I90 to the other end of the current-dividing resistor IN. The slides I89 and I90 are mounted on the same frame I84 that supports the slides I82 and I11, so that all four slides are constrained to move in unison.

It is necessary that the rate of change of the resistors I81 and I88 be different from the rate of change of the resistors IBI and I18 for a given movement of the frame I84, because the shunting of the temperature-sensitive resistors changes the sensitivity in non-linear proportion to the change in the value of the shunt-resistance, whereas the compensating resistors I81 and I88 produce changes in the resistances of the bridge arms in proportion to the displacement of the slides I89 and I90. To

reduce these errors, the resistors I and I8I may be tapered from one end to the other as indicated schematically in the drawing.

As indicated by the scale I86 in Fig. 1, when the frame I 84 is in extreme right position, the sensitivity of the temperature-sensitive resistors 35I and 36I is decreased to one-sixth of their normal value (their value when they are not shunted). On the other hand, when the pointer I85 is juxtaposed to'the A2 mark on the scale I86, the resistors IBI and I16 are fully included in the circuit. The compensating resistors I81 and I88 are so arranged that when the pointer I85 is juxtaposed to the /2 mark on scale I88 to reduce the sensitivity of the resistors 351 and 36I to the compensating resistors I81 and H58 are cut into the circuit to a suificient extent to compensate for the reduction in the resistance of the bridge arms produced by the introduction The values can be calculated by assuming that the sensitivity of the resistors 35I and 36I changes in proportion to the third power of the current (which may be assumed for certain cases). -Assuming further that the temperature-sensitive resistors 35I and 36I have an average resistance of 10 ohms at average operating temperature and.

the normal value of the current in each tern perature-sensitive resistance is 100 milliamperes, the values of the resistors may have the values shown in the following table:

Table of con ugated values of shunt and compensatmg reszstances (m ohms) Reduction of sensitivity 86 9% $5 $4 1 Variable shunts, 176 and 18 0.00 1.63 4.18 9.32 24.57 0 Fixed shunts, 175 and 180 9. 83 9.83 9.83 9.83 9.83 0 Total shunt resistance 9.83 11.46 14.01 19.15 34.40 0 Compensating resistors 187 and 188 5.58 5.24 4. 78 4.11 2.88 0

Current, m. a. in resistors 351 and 361 55 58.5 62.8 69.2 79.3 100 Cinrent through shunt,

m.a 45 41.5 37.2 30.8 20.7 0 Total current, m.a 100 100 100 100 100 100 It is to be understood that the foregoing table should be considered only as an approximate example of the resistance values. In actual practice, the proper values, of the shunt and compensating resistors can be readily determined experimentally when the bridge is divided into two separate bridge circuits by movement of the switch I I6 into positions B and C, respectively.

For example, a mixture of air and CO2 can be flowed to the cells 35 and 36 while air alone is flowed to the pair of cells 31 and 38. Underthese conditions, the deflections produced by the two pairs of cells are equal when the shunts are cut out by opening the switches I83 and I18, and the compensating resistors I81 and I88 are adjusted i to zero value, as shown in Fig. 1.

Thereafter, the shunts are included into the circuit by closing the switches I83 and I18, and the frame I84 is adjusted to move the slides I82 and I11 into that position in which the deflection produced by the bridge X is one-half of its former value. Thereafter, the values of the portions of v the compensating resistors I81 and I88 that are included in the circuit are so chosen that the current through the bridge is restored to its normal value (200 m. a. in the present instance) This operation can be repeated to determine theproper settings of the slides I82 and I11 to pro.

duce reductions of sensitivity of one-third, onefourth, one-fifth and one-sixth, respectively, and

to properly choose the values of the portion of resistors I81 and I88 that are included in the circuit in each position.

It is to be understood that it is not always necessary to make the shunt and compensating resistors adjustable. There are many situations where a fixed value of sensitivity is desired and may be obtained by choosing shunt and compensating resistors of proper value in the first place.

Further in accordance with the present invention, both a desired relative sensitivity of the arms of the bridge and continuous regeneration the'branch' conduit- I58 with air admitted through the conduit, I60. 'In general, the diluent gasshould have a thermal conductivity substantially the same as that of the gaswhich is'present as a diluent in the gas to be measured. I

' In the case of exhaust'gas'nitrogen and oxygen may constitute the diluent gases, and their thermal conductivity is substantially'the same asatmospheric air. V

In practice, when employing dilution'of the exhaust gas in conduit I58 to reduce the sensi-' tivity and regenerate the copper oxide in the treating chamber I65, the valve I6I is opened and the restrictor' I62 is adjusted until the de: sired dilutionis obtained. It may be assumed that the dust I I3 is connected to a suction pump to produce a sub-ambient pressure sufficient "to draw air into the conduit I58- past the 're'st'rictor I62, orthat air under super-ambient pressure is supplied to the inletof the restrictor I62.

The proper adjustment of the restrictor I62 may be obtained as follows: First-with valve l6I closed, the fuel-air ratio of the device I52 is altered by movement of the control handle I52 until the potential produced by'each pair oi temperature-sensitive resistors '3 5 I ,--36 I, and '31 I, 38I is zero, as indicatedby zero deflection of the meter I20, when the switch I I6 is in position D or E. Then the handle I52 is moved an arbitrary distance in the direction to make the mixture lean, and the deflection of tlie'meter I20 is recorded. Thereafter, the handle I52 is shifted thesamearbitrary distance in the opposite' direction from the position-where the theoretical mixture was obtainedso as to make the'mixture rich to the same extent that it was made lean by the previous movement. The d'efiection'of the meter I20 generally will be several times larger for the rich m'ixture than-it was for-the lean-mixture. The operator-then opens the air valve: I 6| and adjusts the restrictor'I62 until the deflection ofthe meter"lZ0 is thes'a'me (but in the opposite direction) as it was-for the previously recorded leanmixture; The system-is-thereby adjusted to indicate equivalent lean and rich mixtures by equal deflections on the meter I20.

It will be noted that the described procedure gives equal deflections for-rich and'lean -mixtures on an ordinary unbiased-meter because the sensitivity of the elements (resistors 35I' and 36I) producing an indication of the hydrogen concentration is reduced without changing 'the' sensitivity of the elements (resistors'31land-381) producing-an indication of the oxyg'en concentration in a leanmixture.

The air admitted through conduit I60 into conduit I63 continuously regenerates any re-' duced ccpper I in chamber 1 I65 Y back to copper oxide. N

In accordance with the invention," stfll another method of reducing the 'se'nsitivity of the cells 35 and 36 is to o en the valve [Ninthediffusion assage 213 'which interconnects' the' cells. This reduces the relative sensitivity of the cells 35' and 36 by automatic selective mixing of the gases within the'two cells.

Thus, it is-well-known that the thermal-conduotivity of a gas 'is' intrinsically dependent on the value of the -diflusion'ct'mstanti'or that gas, so that the diffusion constant is lai'ge when the thermal' conductivity is high. It'follows that where means is provided for transfer by diffusion of gas between the two cells, the reduction of the sensitivity ofresponseis substantially proportional to the value of the thermal. conductivity of the gas having the higher thermal conductivity.

When employing-the diffusion passage 213 to reduce the sensitivity of response of the cells 35 and 36, calibration'can be'efiected in exactly the same manner previously described in connection with the method of reducing sensitivity by dilution, except that whereas by the latter method the variable restrictor I62 is adjusted, in

,the present method the valve I14 is adjusted.

Fig. 2 illustratesthe application'of the invention to the analysis of exhaust gas resulting from combustion'of pure carbon and air. The exhaust gas is first conducted by a conduit 200 past the cell 35 and then through a treating chamber 20I containing hot carbon. From the chamber 20I the gas flows through a conduit 202 past cells'36 and 31 to a treating chamber 206 containing hot copper oxide, from which it flows through a conduit 20'! past cell 36. Air-for dilution can'be admitted into the conduit 202 through a conduit 204 containing a variable restriction203 and a valve 205.

It is obvious, therefore, that cell 35 receives untreated exhaust, cells 36 and 31 receive exhaust'that has been treated with hot carbon to consume any excess oxygen, and the cell 38 is exposed to exhaust'gas that not only has been exposed to hot carbon to consume any excess oxygen, but has also been exposed to hot copper oxide to complete combustion of any car bon monoxide 'to carbon dioxide.

Obviously, the exhaust 'gas from a lean mixture will contain oxygen which, after treatment with heated carbon in the chamber 2!, will be converted into carbon dioxide. Consequently, the potential produced by the'resistors 35I and 36I in cells 35 and 36, respectively, will be proportional to the excess of oxygen.

On the other hand, when the'mixture is theoretical or rich, the hot carbon in the chamber 20I will have no 'efiect on the gas and no potential will be produced by the resistors 35I and 36I Considering cells 31 and 38, the exhaust from a lean mixture will not be afiected by contact withthe hot copper oxide in the chamber 206,

' despite the fact that the exhaust has previously been treated with the hot carbon in chamber 20I. Regardless of whether the mixture is theoretical or lean, all carbon will have been converted to carbon dioxide by the time it reaches the conduit" 202, and hence, for lean and theoretical mixtures there will be no potential produced by the resistors 3' and 38I in cells 31 and 38, respectively.

However, since the'exhaust from a rich mixture will contain carbon monoxide which will react with the hot'copper oxide in the treating chamber 200 to produce additional carbon dioxide, there will be a potential developed by the'resistors 3H and SM of magnitude proportional to the amount of carbon'dioxide additionally formed'by treatment in the chamber 206.

' If the resistors 35I, 36I, 3H and 38I are similar and equally sensitive, the deflection of the meter I20 produced by the additional carbon dioxide resulting from combustion of carbon monoxide in the chamber 206 by contact with the hot copperoxide therein will be twice as large for each per cent of deficiency in oxygen as the deflection produced by the potential developed in the resistors 35I and 36I from the burning of excess oxygen to carbon dioxide in the chamber 20 I.

This is so because half of the oxygen in the carbon dioxide produced by combustion of carbon monoxide with copper oxide in the chamber 206 was contributed by atmospheric air in the original combustion which burned the carbon to carbon monoxide; and only half of the oxygen in such carbon dioxide was contributed by the copper oxide in the chamber 206. On the other hand, all of the oxygen used to generate carbon dioxide in the treating chamber ZOI is derived from the excess atmospheric air present in the original combustion.

In order to express on the same scale of the meter I28 the deficiency of oxygen in the exhaust of a rich mixture and the excess of oxygen in a lean mixture, it is necessary to reduce the potential produced by cells 3! and 38 to one half of the value of the potential produced by the cells 35 and 3B.

In the system shown in Fig. 2, this can be accomplished by opening the valve 205, so that additional air will be mixed with the exhaust gas after it has passed cells 35 and 36. It is presumed that either suction is applied to the conduit 20'! to reduce the pressure therein below the ambient pressure, or that the inlet end of the conduit 204 is connected to a source of air at super-ambient pressure in order to produce the necessary flow of air through the conduit 204 into the conduit 202.

In Fig. 2 the reversal switch 219 is normally in such position that the potential produced by the resistors 35! and 36I in response to carbon di oxide resulting from the combustion of carbon in the chamber 2III is of opposite sign to that produced by the resistors 3H and 38! by carbon dioxide resulting from combustion of carbon monoxide in the treating chamber 206. Consequently, the system disclosed in Fig. 2 indicates, by the direction of deflection of the meter I20, whether there is an excess or a deficiency of oxygen and indicates when the mixture is theoretically correct for complete combustion by giving a zero deflection.

It is an easy matter to adjust the restriction 203 to produce the desired dilution of the gas in the conduit 202. A procedure that may be followed is to deliver a constant rich exhaust mixture to the conduit 200 and observe the deflection of the meter I22 while the valve 205 is closed. Thereafter, the valve 205 is opened and the restriction 203 is adjusted until the deflection of the meter I29 is reduced. to the desired value, which, in this instance, will be one half of its normal value when the valve 205 was closed.

In the arrangement of Fig. 2, as in the arrangement of Fig. 1, the dilution of the exhaust prior to its treatment with the hot copper oxide serves to regenerate any reduced copper therein.

When a rich mixture containing no free oxygen is admitted to a chamber containing hot copper oxide, a portion of the latter near the entry end of the chamber is usually first reduced to copper, and if rich exhaust is admitted to the chamber for a long time all of the copper oxide may be reduced to copper, whereupon the apparatus becomes inoperative.

However, by diluting the exhaust with an equal volume of air, the apparatus becomes for all practical purposes operative for an indefinite period of time, since the oxygen of the air regenerates any reduced copper back to copper oxide. An incidental advantage of employing continuous regeneration of the copper oxide is that it prevents deposit on reduced copper of carbon and gummy substances in the exhaust. Such deposits subsequently burn and upset the balance when the mixture later becomes lean.

It has been noted that in the system of Fig. 2 the reversing switch 210 should be positioned so that a lean mixture produces a potential which deflects the hand in the opposite direction from that in which it is deflected by a rich mixture. However, if the reversing switch 210 is in the opposite position, the theoretical mixture will still give a zero reading on the meter I20, but both lean and rich mixtures will deflect the needle away from zero in the same direction, although to equal extent.

It is also of interest to note that in Fig. 2 only one side of the circuit is abnormal at any given time. Thus, the potential produced by the resistors 35I and 3BI in one pair of opposing arms of the bridge is affected by a lean mixture but not a rich mixture. On the other hand, the potential developed by the resistors 3H and 38I in the other pair of arms of the bridge is affected by a rich mixture but not by a lean mixture.

Fig. 3 illustrates the application of the invention to the analysis of exhaust gas from combustion of carbon containing sulphur. The exhaust gas may be delivered by the conduit 22!! through a treating chamber 22! which may contain agents for completing combustion of combustible gases and removing water. From the chamber 22I the gas is conducted by a conduit 222 past the cell 35 and to a treating chamber 223, which contains .an agent, such as lead peroxide, that is capable of removing sulphur dioxide from the exhaust gas. After being treated in the chamber 223, the exhaust gas is delivered to a conduit 224 which conducts it past the test cells 36 and 3'! to a treating chamber 22! containing an agent capable of absorbing carbon dioxide, such as potassium hydroxide. From the treating chamber 221, the gas is delivered to a conduit 228 which conducts it past the test cell 38. After the gas has passed chamber 221 both the variable components (sulphur dioxide and carbon dioxide) have been eliminated. Therefore, if desired, the chamber 221 can be dispensed with and a fixed reference gas such as air can be sealed in the test cell 38.

The system shown in Fig. 3 is particularly useful for analyzing the products of combustion of fuels such as coal, which frequently contains sulphur, so that the exhaust of the fuel contains sulphur dioxide in addition to carbon dioxide. The eifect on thermal conductivity of one per cent of sulphur dioxide is in the same direction and nearly three times as great as the effect of one per cent of carbon dioxide. Accordingly, considerable errors occur in analyzing the exhaust of coals containing sulphur by ordinary thermal conductivity methods, particularly if the percentage of sulphur in the coal varies.

In the past, it has been common practice to remove sulphur dioxide from exhaust gas prior to admission of the gas to the cells of a thermal conductivity gas analyzer. Obviously, when this is done, the apparatus does not take into account the amount of oxygen consumed in combustion of the sulphur in the fuel.

The system shown in Fig. 3 enables the measurement of the oxygen consumed in combustion of both the sulphur and the carbon.- Thus the resistors 35I and 36I in one pair of op posing arms of the bridge produce a potential proportional to the amount of sulphur dioxide in the exhaust, which potential tends to shift The resistors 31! -and 38l produce a potential proportional to-- the amount of carbon dioxide present in the exhaust gas, and the reversing switch 210 is positioned as shown in full lines so that this potential deflects-the hand of the meter I20 in the said one direction. Therefore, the total deflection of the meter hand is the summation effect of both; the carbon dioxide and the sulphur dioxide-in the exhaust gas- However, in order for the sulphur dioxide and the carbon dioxide to both produce effects on the meter I20 that are proportional to the amount of oxygen consumed in their production, the responseof the meter to agiven percentage of sulphur dioxide is reduced to approximately one third of its normal value. This is done in the circuit of Fig. 3 by provision of suitable fixed shunts 235 and 236 connected to the temperature-sensitive resistors 35! and 36L respectively, and fixed resistors 231 and '238 connected in series in the respective arms of the bridge. In other words, the shunts 235 and 236 and the series resistors 23! and 238 of Fig. 3 perform the same function as the adjustable shunt and series resistors of Fig. 1.

The situation described with reference to Fig. 3 is characteristic of a large class of situations in which the gas resulting from action with a first agent (lead peroxide in this particular instance) has a thermal conductivity intermediate between that of the original gas and that of the gas obtained after treatments with a second agent (potassium hydroxide in this particular instance).

The method and apparatus is not confined in its usefulness to the analysis of the exhaust gas from coal containing sulphur and it is not confined to the specific reagents indicated, but is applicable to all systems in which the thermal conductivity of the gas resulting from the first treatment is intermediate the thermal conductivity of the original mixture and the gas obtained after a second treatment. Obviously, the ratio between the sensitivities of the two opposing pairs of resistors should be so chosen as to reduce the effects to a common scale.

It should be noted particularly that the system of Fig. 3 is distinct from that disclosed in my application, Serial No. 564,645, in which arithmetical summation of the effects produced by water vapor and carbon dioxide is utilized in the analysis of exhaust gas resulting from burning of hydro-carbons.

The distinction is of a two-fold nature. In the first place, sulphur dioxide and carbon dioxide affect the thermal conductivity of exhaust gas in the same direction, whereas carbon dioxide and water vapor produce opposing effects on the thermal conductivity of exhaust gas. In the second place, the effects on thermal conductivity produced by carbon dioxide and water formed from the same amount of oxygen may be assumed to be equal in magnitude, whereas the sulphur dioxide formed from one volume of oxygen affects the thermal conductivity to about three times the extent that the carbon dioxide formed from the same amont of oxygen does.

It is to be noted that the system of Fig. 3 differs from that of Fig. 2. in the following respect: In Fig. 2, the left and righthalves of the, bridgebecome effective consecutively as the mixture varies from rich to lean or vice versa, but both halves of the bridge do not vary in value v simultaneously. In contrast, both the left and right halves of'thebridge in Fig- 3 may vary simultaneously.

As a result of this, the system of Fig. 3 can be employed to not only obtain the total amount of oxygen consumed or required for the consumption of both the carbon and the sulphur, but can be used to obtain the relative amounts of carbon and sulphur in the fuel. Thus, when the reversing switch 210 is in the solid line position as described, the amounts of oxygen required for the production of the carbon dioxide and the sulphur dioxide, respectively, are added, after reduction to a common scale by means of the shunts 236 and 23?. However, by throwing the reversing switch 210 into its other (dotted line) position, the effect of the sulphur diom'de is subtracted from that of the carbon dioxide. This yields two equations, as previously described in connection with Fig. 1, from which the relative amounts of carbon and sulphur can be determined.

The present invention further distinguishes from that disclosed in my application, Serial No. 564,645, in that my present invention provides for the determination of the concentration of one component of a parent substance when its presence is manifested by two gaseous components, such that the ratio of their effects on the thermal conductivity of the gas is different from the ratio of the amounts of the parent substances required forthe formation of said components. w

In contrast, the prior application, Serial No. 564,645, is limited to the particular situation in which oxygen of the air burns hydrocarbons to water and carbon dioxide. By a fortunate circumstance, each volume of .oxygen forms one volume of carbon dioxide and two volumes of water, but the two volumes of Water produce the same absolute effect (disregarding sign) as one volume of carbon dioxide.

In most situations, such a simple relationship consumption of a given amount of oxygen does not exist, and the components of a gaseous mixture resulting from interaction of parent substances will usually affect thermal conductivity to extents not proportional, to the amounts of the common parent substance required for their formation, as evidenced by the example of carbon dioxide and sulphur dioxide which has been discussed.

As another example, hydrogen and carbon interacting with an excess of oxygen will produce .only carbondioxide and water, but may produce water and free hydrogen when there is insufiicient oxygen forcomplete combustion. In such a situation, the oxygen concentration in a lean exhaust will be proportional to the excess of oxygen in the mixture, but of itself will produce.

y a small effect on the thermal conductivity, which for many purposes is negligible because the thermal conductivities of oxygen and nitrogen are nearly thesame.

However, in a rich exhaust the deficiency of oxygen may be indicated by free hydrogen, which produces a great effect on the thermal conductivity of the exhaust. Thus, the hydrogen component in the exhaust isindicative of a deficiency.

of oxygen, although it does not contain any oxygen.

The systems so. far described with reference toFigs. 1, 2,. and 3 permit adjustment to attain.

because; as shown in the curves 'in'Fig. 13 of my four times as great for rich mixtures as lean.

mixtures.

For convenience of language in the claims, the expression opposing resistors has been used in referring to resistors in certain arms of the bridge circuits. In Figs. 1, 2 and 3, the resistors 35| and 36| are in one pair of opposing arms, and the resistors 3H and 38! are in another pair of opposing arms. The expression opposing resisters" used in the claims, means any two resistors of the bridge in which similar resistance changes in the same direction tend to neutralize each other in their effect on the meter of the bridge circuit.

Although for the purpose of explaining the invention, certain specific embodiments thereof have been described in detail, it is to be understood that various changes and departures can be made from the particular constructions described without departing from the invention which is to be limited only to the extent set forth in the appended claims.

I claim:

1. In a gas analysis system of the type described: a bridge circuit having two pairs of opposing temperature-sensitive resistors in which the sensitivity of the resistors in one of said pairs is difierent from the sensitivity of the resistors in said other pair, and said bridge circuit includes a reversing switch for reversing the positions in said bridge of the two resistors constituting one of said pairs and means for exposing the resistors of each pair to a different sample of gas, said means including at least one duct for leading gas from a stream into exposing relationship with the resistors of one pair.

, 2. In ,a gas analysissystem of the type described, abridge circuit having a first pair of opposing temperature-sensitive resistors and a second pair of opposing temperature-sensitive resistors; first means for exposing the resistors of said first pair to samples of a gas for producing a temperature differential therebetween, and second means for exposing the resistors of said second pair of opposing temperature-sensitive resistors to samples of gas for producing a temperature diiferential therebetween, said bridge responding to a combination of said temperature differentials; and switch means for interchanging the positions in the bridge circuit of the two resistors constituting one of said pairs, while said temperature differential therebetween are maintained, whereby said bridge circuit is adapted to successively indicate the sum and difference respectively of said two temperature differentials. I

,3. A system as described in claim 2 including separate compensating resistance means connected with each of said pairs of resistors for separately neutralizing an unbalancing effect on said bridge of either of said pairs of resistors.

4. In a system of the type described, a bridge circuit having: a first pair of thermal-conductivitycells containing temperature-sensitive resistors in opposing relation in said bridge and means for supplying to said cells two gases distinguishing from each other by one component; a second pair of thermal-conductivity'cells containing temperature sensitive resistors connected in opposing relation in said bridge, and means for supplying to the respective cells of said second pair two gases distinguishing from each other by another measurable component, whereby the effects of said two measurable components are compared by the bridge; and means for controllably reducing thetemperature differential between the resistors in one of said pairs of cells resulting from the change in thermal-conductivity caused by a change in the concentration of one of said measurable components, said lastmentioned means comprising means for diluting the gas supplied to one of said pairs of cells.

5. In a system of the type described, a bridge circuit having: a first pair of thermal-conductivity cells containing temperature-sensitive resistors in opposing relation in said bridge and means for supplying to said cells two gases distinguishing from each other by one component; a second pair of thermal-conductivity cells containing temperature-sensitive resistors connected in opposing relation in said bridge, and means for supplying to the respective cells of said second pair two gases distinguishing from each other by another measurable component, whereby the effects of said two measurable components are compared by the bridge; and means for control;- lably reducing the temperature differential between the resistors in one of said pairs of cells resulting from the change in thermal-conductivity caused by a change in the concentration of one of said measurable components, said last mentioned means comprisingmeans defining a diffusion passage interconnecting one of said pairs of cells.

6. In thermal conductivity gas analysis apparatus: a bridge having first and second pairs of opposing arms containing electrically heated temperature-sensitive resistors disposed in test cells and means for supplying gases to be compared to said test cells; shunt variable resistance means connected in shunt to the temperaturesensitive resistors in one pair of opposing arms; series variable resistance means connected in series in said pair of opposing arms; and means for simultaneously varying said shunt and series resistance means in such relation as to maintain the total current in each arm substantially constant while varying the portion of the current in each arm that traverses the temperature-sensitive resistor therein.

7. A gas analysis system comprising: four thermal-conductivity cells arranged in first and second pairs, respectively, said first .pair. of cells having temperature-sensitive resistors connected, respectively, in a first pair of opposing arms of a bridge and the second pair of cells having temperature-sensitive resistors connected in a second pair of opposing arms of the bridge; a source of exhaust gas and a first conduit connected thereto; second and thirdconduits connected in parallel and to said first conduit; fourth and fifth conduits connected in parallel and to said second 'conduit for supplying gas to said first pair of cells, sixth and seventh conduits connected in parallel and to said third conduit for supplying gas to said second pair of cells; and

means arranged in said fourth and sixth conof saidbridge; i

8."Ga's analysis apparatus comprising: four 21 test cells for receiving gas to be analyzed, each cell having an electrically heated test resistor, the resistance of which varies with temperature and the temperature of which varies according to the thermal conductivity of gas in the cell; four fixed comparison resistors; a current limiting resistor; a source of current; potential responsive means; switching means operable into four different positions and having a plurality of contacts so disposed and so connected to said resistors, source of current, and potential responsive means that bridge circuits are created, in which: in a first position of said switch, one pair of said test resistors are in one pair of adjacent bridge arms, and one pair of said comparison resistors are in the other pair of adjacent bridge arms; in a second position of said switch, the other pair of test resistors are in one pair of adjacent bridge arms, and the other pair of comparison resistors are in the other pair of adjacent bridge arms; in a third position of said switch, said one pair of test resistors and said one pair of comparison resistors are in one pair of adjacent bridge arms, and the other pair of test resistors and the other pair of comparison resistors are in the other pair of adjacent bridge arms; and in a fourth position of said switch, said one pair of test resistors constitute one pair of adjacent arms of said bridge and the other pair of test resistors constitute the other pair of adjacent arms of said bridge.

WLADIMIR M. ZAIKOWSKY.

REFERENCES CITED The following references are of record in the file of this patent:

22 UNITED STATES PATENTS Number Name Date 1,206,968 Wilsey Dec. 5, 1916 1,530,202 Rodhe Mar. 17, 1925 1,644,951 Rodhe Oct. 11, 1927 1,681,047 Porter Aug. 14, 1928 1,707,624 Brown Apr. 2, 1929 1,715,374 Krueger June 4, 1929 1,829,649 Harrison Oct. 27, 1931 1,981,172 Harrison Nov. 20, 1934 2,000,119 Brown et a1. May 7, 1935 2,005,036 Howe June 18, 1935 2,042,646 Willenborg June 2, 1936 2,050,878 Dallman et a1 Aug. 11, 1936 2,053,121 Vayda Sept. 1, 1936 2,135,587 Lovelady Nov. 8, 1938 2,175,890 Glowatzki Oct. 10, 1939 2,204,966 Morgan et al June 18, 1940 FOREIGN PATENTS Number Country Date 283,667 Germany Aug. 12, 1913 373,239 Germany Mar. 4, 1922 425,518 Germany July 1, 1924 494,754 Great Britain Oct. 31, 1938 883,420 France July 5, 1943 OTHER REFERENCES Book-Gas Analysis by Measurement of Thermal Conductivity, by Daynes. Published-Cambridge University Press 1933. 

